/Engine/Source/Runtime/Core/Public/Containers/Map.h
Add all items from another map to our map (if any keys are in both, the value from the other map wins).
template<typename OtherSetAllocator> void Append ( const [TMap](API\Runtime\Core\Containers\TMap)< [KeyType](API\Runtime\Core\Containers\TMap\KeyType), [ValueType](API\Runtime\Core\Containers\TMap\ValueType), OtherSetAllocator, KeyFuncs > & OtherMap )